The invention is directed to the heat protection of structure surfaces and components (such as structure surfaces and components of aircraft, aero structure surfaces, engine, missile and rocket components) which are exposed to high temperatures, such as temperatures 650° F.-2000° F., Traditionally these structure surfaces and components are made from high temperature metal alloys. High temperature metal alloys are generally high density and add weight to the aircraft, aircraft engine or missile and rocket structures. Alternatively, or in addition, these structure surfaces and components are heat shielded by being covered with a heat protective material. For complex component surfaces, however, such heat shielding can be difficult to apply and maintain.
PMC's (polymer matrix composites) have been used as a lighter weight alternative for metal structures in aircraft, aircraft engine, missile and rocket applications. PMC's have high tensile and compressive properties making them an appropriate replacement for titanium structures in a high stress environment. Some PMC's (e.g., polyimide PMC's) provide effective heat shielding up to about 650° F. PMC's cannot, however, provide effective heat shielding above 650° F.
Oxide ceramic composites (Ox/Ox CMC's), on the other hand, can be used to provide effective heat shielding in applications up to about 2000° F. Ox/Ox CMC's have high temperature resistance and very low thermal conductivity, but have relatively low compressive strength and are difficult to attach due to their low bearing strength.
Heat shielding with some form of high temperature PMC/CMC hybrid is possible, but there are problems associated with such hybrid structures. Because the thermal expansion rates of Ox/Ox CMC's and PMC's are markedly different, as the hybrid structure heats up, the mismatch in thermal expansion causes the Ox/Ox CMC to delaminate and disbond from the PMC. This delamination problem limits the maximum size for PMC/CMC hybrid surfaces. The ability to use PMC/CMC hybrids has been limited to small structures, whereas, some jet engine structures, such as exhaust ducts, may require components over 60 inches long and 50 inches in diameter.
Assembling small Ox/Ox CMC tiles into a tessellated pattern attempts to deal with the size issue, but does not completely solve the thermal protection challenge. As illustrated in FIG. 1, Ox/Ox CMC tile patterns 2 relying on butt joints 4 are inadequate because the mismatch in thermal expansion rate causes butt joints to separate—thereby allowing hot gases 6 to readily penetrate the Ox/Ox CMC 2 tile layer to reach the PMC layer 8. Tile patterns relying on lap joints seem possible, but no lap laminate pattern has been suggested which has suitable overlap joints on all sides of the laminate, while keeping the overall size of the Ox/Ox CMC tile to a minimum.
There is a need, therefore, for a high temperature composite which avoids the aforementioned problems in the prior art.